pthread_setname_np is a can of worms for portability. Linux, macOS,
and the BSDs all do it differently.
Also skip adding the tid as an inspectable Core::Object property on
systems where pthread_t is known to be a pointer.
Users can now determine whether a thread has been started or not. A
started thread might also have already terminated.
Implementation note: We *could* detect this with pthread APIs maybe, but
this is much simpler.
Each of these strings would previously rely on StringView's char const*
constructor overload, which would call __builtin_strlen on the string.
Since we now have operator ""sv, we can replace these with much simpler
versions. This opens the door to being able to remove
StringView(char const*).
No functional changes.
Sometimes you don't care about `joining()` the result of a thread. The
underlying pthread implementation already existed for detaching and
now we expose it to the higher level API.
